In United Kingdom Patent No. 2,144,244 B, positive longitudinal pitch rate is used to indicate high rotor load factors, such as during high speed highly banked turns. At high speed, some shaping of pitch rate is accomplished to provide a signal to be added to the normal engine reference speed signal, such as to command a higher engine speed. In said patent, it is also suggested that a signal derived by shaping the output of a vertical body axis accelerometer could also be used to enhance engine speed during heavy rotor load maneuvers, either alone or in conjunction with the shaped pitch rate signal. In said patent, it is stated that increasing the engine speed reference provides higher rotor thrust while preserving rotor stall and control margins during high rotor load maneuvers.
It has been found that using a shaped signal of the event in question tends to abruptly reduce the engine speed near the end of the high rotor load maneuver, inducing yaw transients which are highly undesirable at precisely the point where stability is desired, adding significantly to pilot workload. Further, using such a shaped signal tends to cause the engine to achieve speeds in excess of reference speeds under heavy load, thus causing a tendency toward exceeding maximum permissible torque in the engine. Any advantage that the pilot workload may gain because of the speed enhancement is diminished by the need to constantly monitor the torque, providing load-relaxing inputs to the blade pitch controls, or beeping speed down during the maneuver. All of this tends to increase instability and increase pilot workload and therefore is unfavorable.